The parts kit comes with the wrong wheels. The wheels have a v in them and they should not have it. Especially the wheels that guide the belt over the stepper motor. I saw something about sending random wheel types but that is like saying that you will randomly send the wrong parts. What is wrong with you? This is no way to sell a product.
Why are you knowingly sending out the wrong parts? Because you didn't have the right ones in stock or you just happened to have a bunch of the wrong wheels left over from a different product so you thought you would use them up. This is what's wrong with Chinese products! They always fall apart or arrive with missing, wrong or defective parts. Don't you care about your customers? Since I can;t wait 3 or 4 weeks for you to send the correct parts (if you even will) I'll have to use some wheels from my 3D printer parts. This is not right!